You are correct that Automation Studio is more an Integration Platform
If you are looking to write custom apps you are going to want to go with the REST interface or look at a product like Bezlio https://bezl.io/ (for mobile apps)
Epicor also has their own mobile apps EMWW and like @jgiese.wci the Magento Ecommerce Solution. There is also Part Trap (https://www.parttrap.com/) which I know has an Epicor integration, Sales Force for CRM Epicor has integration with them both via Automation Studio and in Kinetic Native
Really with Kinetic the possibilities are endless you have a fully supported end to end REST Interface, the entire platform is written on an Service Oriented Architecture so most functionality, field and button click can be reached with a service
If you have some more specific requirements we could give you more specific recommendations. I will say Automation Studio is a pretty great tool we are very glad to have gotten (more technical details can be found on this site, also @timshuwy is the Product Owner over there and willing to answer any and all questions you may have)